Owners of personal watercraft, such as small boats, canoes, dinghies, jet skies, and similar marine craft, frequently launch and retrieve their watercraft from a dock or pier. To assist in these tasks, there have been developed watercraft lifts that mount on the dock. These dock-side lifts enable the owner or user to gently lower the watercraft into the water and easily and quickly remove the same from the water.
An example of such a lift is disclosed in U.S. Pat. No. 5,143,182, issued to Samuel T. Basta on Sep. 1, 1992, for a Low-Profile Watercraft Lift. As disclosed therein, the lift includes a base mounted on a dock and a load-bearing member attached to the base. The load-bearing member depends downward adjacent the dock and partially into the body of water. A carriage mounted on the load-bearing member moves up and down relative to the water as controlled by a winch on the top of the load-bearing member. This apparatus is mounted on the top surface of the dock and has no attachment to the side of the dock and no support on the floor of the body of the water.
Another device is disclosed in U.S. Pat. No. 4,983,067, issued to Montgomery on Jan. 8, 1991, for a Boat Lift Apparatus. This apparatus is mounted on the top and on the side of a dock and extends downward into the water. A load-bearing member is secured to a piling upholding the dock for lateral stability. In addition, the load-bearing member is shown anchored to the floor of the body of water by an extendable tube mounted inside a rail. The drawback to this device is that bracing to the dock is required for vertical stability. Another drawback is the lack of attachment between the extendable inner tube that is anchored in the floor and the rail portions in which it is mounted. In order words, it is possible for the lift apparatus to be raised up while the inner tube is anchored in the floor of the body of water. Thus, heavy loads exerted on one side of a portable dock may cause the portable dock to twist or otherwise move in an undesirable fashion. The apparatus of Montgomery would fail to prevent such movement because the anchored inner tube is not attached to the load member.
In addition, U.S. Pat. No. 4,678,366, issued on Jul. 7, 1987, to Williamson for a Boat Lift shows a vertical H-beam driven into the floor of a body of water adjacent a pier. The H-beam is used as a track on which a shaft housing and boat lift slides up and down. Williamson does not teach or suggest the use of an optional support leg for supporting the boat lift on the floor of the body of water. Rather, the load-bearing member, i.e., the vertical H-beam, is itself driven directly into the floor of the body of water. This device makes no provision for variance in the depth of the water and the height of the dock because the dock is a fixed structure.
Consequently, there is a need for a watercraft lift that is adequately anchored in the floor of a body of water when mounted on a portable dock and fixedly attached to the lift while permitting adjustment for variance in dock height and water depth.